Abstract: A hydroplane boat hull of cylindrical-ellipsoidal form formed from sections each having internal flanges formed around the edges thereof, the abutting flanges of the sections being secured together to form the hull and at the same time the flanges forming internal ribs for the hull. The hull includes a keel including an engine supporting base having a step formed thereon, a step providing a planing surface for the hull. A pair of propellor housings are joined to the engine supporting base, they extend longitudinally thereof and each propellor housing has an opening located adjacent the step so that as the hull rises to a planing position on the step the propellors constantly engage the water.